Metso reports current developments and the future direction of its RFID-based ore tracking system
A significant amount of the consulting work performed by Metso’s Process Technology and Innovation group involves Process Integration and Optimization (PIO) studies, which includes investigating the effects of drill and blast design and implementation on downstream processing. Critical to these studies is the ability to track specific ore into and through the plant.
To increase the accuracy of this ore tracking, Metso Process Technology and Innovation (PTI) developed a system to track ore using RFID transponders called SmartTag. Since its commercialization in 2007 SmartTag has been used in the majority of PTI’s consulting projects and several permanent systems have been installed worldwide.
According to PTI, the benefits of using SmartTag include: linking spatial mine data to time-based processing data; increased confidence in ore blending; proactive process changes for known ore types; and accurate measurement of residence times in stock piles and bins.
Since 2007, there have been significant advancements with RFID technology that have allowed PTI to extend the reach of SmartTag beyond secondary crushing to tertiary crushing and even further downstream. This has been achieved by drastically reducing the size of the SmartTags from a diameter of 60 mm to 20 mm. The new smaller RFID tags have been successfully used in several studies.
The SmartTag System
A SmartTag RFID tag travels through a mine and mineral processing plant in a series of simple steps. Initially, the tag and insertion location is logged using a handheld computer or PDA, then it is inserted into the ore (e.g., into a blasthole). The tag travels with the ore through digging, transport and processing before being detected at specific locations on conveyor belts, when the time and specific tag is recorded. The RFID tag data is then loaded into a database and analyzed as required.
To achieve this, the SmartTag system requires five main components: The first is a PDA, which allows the initial RFID tag insertion process to become more efficient and accurate. Each RFID tag is added to the database using one of three options—it is associated with a GPS coordinate; it is associated with a predefined point (such as a blasthole); or it is associated with a new point, which can be accurately located later.
Currently, the system does not allow for high-precision GPS but it can locate the nearest point in a series of predefined points, such as blastholes, and allow the user to associate RFID tags with these points.
The next component in the system, the antenna, is located at the conveyor belts. The antenna both induces a charge on the tag and also receives a transmitted signal back from the tag. The design of the antenna is decided by two parameters, which are its size and its robustness. The size of the antenna dictates the size and the strength of the field it radiates. For this application the area of field strong enough to charge the tag should be as large as possible; therefore, the antenna used for the SmartTag system is the largest available for this frequency of RFID system.
An RFID reader then decodes the signal from the antenna and determines the ID of the RFID tag passing the antenna. Later versions of the readers also have auto-tuning capabilities which ensure that the maximum possible read distance is achieved at all times. In the SmartTag system the reader then transmits the ID using serial communications.
A data logging or buffer stage improves the reliability of the systems and also makes movable systems possible. The data logger receives data directly from the RFID reader, stores the IDs with the time they were detected and monitors vital system parameters, such as the tuning state of the antenna. The data logging stage also makes SmartTag less reliant on communication links (such as wireless) as the data are stored at the detection point until a link is established to the software applications. The critical communications links, such as the link between the antenna and the reader, are all wired and reliable.
The core of the SmartTag software is an SQL (Structured Query Language) database. The database, located on a dedicated server, stores all of the information about the detection points, detected RFID tags and original locations. There are several SmartTag software applications which either input data into the database or use the data to output information. These include the SmartTagServer, which reads data from the data loggers; the SmartTagPDA, which exchanges data with the PDAs and translates site blasthole layout diagrams; and the SmartTagRes, which calculates the residence time between two detection points.
Adding Mini Tags
To expand the applications of SmartTag through and beyond secondary crushing, a mini RFID tag was required. To incorporate the mini RFID tags into the SmartTag system, PTI faced two significant challenges; first, the reduced read distance; and second, making the mini tags robust.
By reducing the size of the RFID tag, the size of the antenna in the tag is also reduced. The size of the antenna in the tag is directly proportional to the amount of charge that is induced for a given field strength. Therefore, the read range of a tag will be reduced as the size of the tag is reduced.
Through investigation, the 20-mm tags were found to have an insufficient read range for the standard SmartTag installation. PTI trialed two methods for fixing this issue; one method was to use two antennas while another was to place the antenna closer to the RFID tags.
Both systems were tested at an iron ore mine. Both approaches, dual antennas or closer antenna distance, were found to have similar detection capability. However, based purely on the ease of installation, a single antenna located under the belt was chosen as the new standard installation method.
The second challenge faced when incorporating the mini RFID tags into the SmartTag system was how to protect them sufficiently to survive a blast. A method previously used by PTI to achieve this was to encase the tags in a two-part epoxy. The method works well for protecting the tags, and although it is time-consuming and expensive it is currently the preferred method for protecting the tags. Different encasing materials, such as reinforced nylon, are still being investigated.
After encasing in epoxy, the mini-tags have a diameter of 20 mm and are shown, with a standard SmartTag as reference, in Figure 1. The size of the mini RFID tags allows them to pass easily through screens with apertures down to 25 mm.
Metso PTI has successfully incorporated a smaller, or mini, RFID tag into their SmartTag system. The changes to the system installation are minor and increase the reliability of the system as a whole. In several examples the mini RFID tags have proven to be, on average, more robust than normal sized RFID tags.
The PTI team envisage that with the successful incorporation of the mini RFID tags into the SmartTag system it will allow applications for the system to be expanded. These new applications could include a wider use in the iron ore industry where size is the critical material quality. PTI is now working on proving the reliability of the next size of RFID tags—an even smaller micro RFID tag, which can pass through a 10-mm mesh screen.
According to PTI, with the decreasing size of RFID tags and the development of SmartTag into a truly distributed system, it can be extended past the mine to cover the whole minerals supply chain. Detection points can now be located in the plant, the port and even at customer locations.
In Some Cases, Smaller is Better
The two case studies presented below demonstrate applications where it was advantageous to use the mini RFID tags rather than the normal size RFID tags.
Secondary Crushing Circuit
As part of a wider PIO study a secondary crushing circuit was surveyed while being fed with a particular ore type. To determine the origin of the ore at any particular time and, most importantly, during the surveys, SmartTag detection points were set up at three locations around the circuit. The three locations were primary crusher product, secondary crusher feed and secondary crusher product.
A total of 384 mini RFID tags were placed on eight polygons (a polygon is defined as different ore zones within the mine block model) after the blast, the ROM pad and trucks as they tipped ore into the primary crusher.
Of the 384 tags placed onto either the muck pile or on the ROM pad, 45% were detected. However, if this is compared with the percentage of each polygon that had been excavated by the end of the trial it is a fair conclusion that many of the RFID tags that weren’t detected were also not excavated during the trial.
To determine the survival rate of the tags during secondary crushing, the number of tags detected before and after the secondary crusher were compared. Of the 128 tags detected before the secondary crusher, 97 were also detected after secondary crushing.
However, as there were 52 tags that were detected after the secondary crusher but weren’t detected before the secondary crusher, the real survival rate is difficult to determine. By just comparing RFID tags detected at both detection points, it can be concluded that at least 76% of the mini tags survived secondary crushing, although this number is likely to be much higher.
The screen immediately following the secondary crusher uses panels with 55-mm apertures and, as expected, none of the tags were recycled back through the secondary crusher.
The primary application for SmartTag was to determine the origin of the ore being processed during the plant surveys. In this application, where the plant feed included ore from ROM mixing and stockpiles, SmartTag was essential for determining which materials were processed in the plant at the time of the surveys. Mini tags were required to enable the ore source to be tracked all the way through secondary crushing, and proved to be robust enough to survive both blasting and secondary crushing.
PTI was contracted to assess the performance of a circuit at a mine in South America. The SmartTag system was used in this application to allow PTI engineers to know exactly when a surveyed blast was being processed. For this reason, detection points were located on conveyor belts carrying the product of the primary crusher, the output of the stockpile and the HPGR (High Pressure Grinding Roll) feed.
As the blast was being audited RFID tags were deposited into 68 blastholes, using an even split of 34 normal tags and 34 mini tags. A further 50 tags were later added into the trays of 25 trucks at the primary crusher, using one of each of the two different types of tags in each truck.
A total of 68 tags were identified at the primary crusher product detection point, 23 at the stockpile output detection point and 41 at the HPGR feed detection point.
The blast occurred January 22 and the excavation of the muck pile took place roughly two months later between March 15–17. The SmartTag system monitored the material passing through the process over a period of 30 hours. During this period, a total of 67 different tags were detected; 33 were of normal size and 34 were mini tags.
For the stockpile and HPGR feed detection points, the recovery was calculated with reference to the 64 distinct RFID tags detected at the primary crusher. Of the normal tags detected at the primary crusher detection point, 42.4% were then detected at the HPGR feed detection point; whereas for the mini tags 67.6% of tags detected at the primary crusher were also detected at the HPGR feed. This shows that the survival of the mini tags in the circuit is higher than the normal tags. In a hypothetical situation, where the secondary screening mesh is smaller than 50 x 50 mm, normal tags certainly would not reach the HPGR.
The detection of tags at the primary crusher was also affected by the removal of the SmartTag system before the entire blast was processed for logistical reasons.
The tags were used to track the material during an optimization campaign at the plant. During the plant survey the material that fed the plant originated from the central portion of the blast.
An unexpected result was that three of the mini tags were twice detected at the HPGR feed detection point. An explanation for this is that they survived the HPGRs and returned with the circulating ore (screened to +5 mm).
This article is based on a paper presented at the 35th APCOM Symposium 2011 in Wollongong, Australia. For additional information, contact Michael Wortley, general manager, PTI Products, Metso Process Technology & Innovation, [email protected].